Reactive Coarse Grained Force Field for Metal-Organic Frameworks Applied to Modeling ZIF-8 Self-Assembly

Decoding the self-assembly mechanism of metal-organic frameworks (MOFs) is a crucial step in reducing trial-and-error tests in their synthesis protocols. Atomistic simulations have proven essential in revealing molecular-level features of MOF nucleation, but they still exhibit limitations due to size constraints, such as inability of reaching realistic concentrations or exploring nonstoichiometric metal:ligand ratios. In this contribution, we develop a methodology to derive reactive coarse grained force fields based on the multiscale coarse graining method. We apply our methodology to the case of the archetypal zeolitic-imidazolate framework ZIF-8. Our coarse grained force field, which we call nb-CG-ZIF-FF, does not contain any explicit connectivity information, but learns the tetrahedral Zn-connectivity from many body correlations within an atomistic benchmark. nb-CG-ZIF-FF quantitatively reproduces the features of bulk, crystalline ZIF-8 as well as the structural evolution of prenucleation species in terms of Zn n-fold coordination populations. While the range of rings that are formed along the synthesis process is well captured by nb-CG-ZIF-FF, the model cannot reproduce ring populations trends. Our reactive CG force field fitting approach can be applied to any MOF, opening new research avenues in modeling MOF formation, decomposition, defect dynamics and phase transition processes.